The preupgrade process leaves all your main settings intact--including filesystems, etc. Since I want to move from ext4 to btrfs, and I want to remove LVM (I have HW Raid on my laptop and do not need LVM) the preupgrade won't work for me.

Understood. I have so much time/effort invested in my system that I don’t want to have to go back and redo all that stuff. It’s not any one thing - it’s just the totality of getting the system into a state where it works for me. I’d hate to reinvent that wheel - I could do it - but I wouldn’t want to.